Sorry James, I can't answer your question as I have the lazy option which is a skinny pedal for forwards and backwards and a fat pedal for stop!
This will make all you diesel drivers feel better at present I'm at 19.8mpg....although I have hit the dizzy heights of 30.0 mpg, but that was after a 2 hour slog up the M6!
Ode to the Vel Satis 3.5v6.
Oh woe is me,
Travelling round town in a Vel Satis,
15.6mpg is all it be,
Picking up me chipatti's.
"Put your foot down!"
They all scream and shout,
I said "Shut up, you clown"
"It costs in this to get about".
But lo, brighter days here,
After wise man said "Convert thy beast",
LPG is nary dear,
North, South, West or East.
So down t'garage did I drive,
Heart in throat and knocking knees,
"Cowboy shop!" said the wife,
I said, "Don't be daft, just a bit of grease".
Three days later I got the call,
"Come t'garage, it's ready."
So down I went nervous as all,
And there it was, rock steady.
"Tha's lost a bit a booit space"
Said cowboy picking nose,
"Gas is still cheap nowadays"
"OK, let's see how it goes".
So off I went to hit the road,
Very gently and taking it slow,
Listening carefully and ¤¤¤¤ting my load,
In case the whole thing should blow.
Two weeks later and I'm whizzing around,
15.6mpg the order of the day,
3 and a half litre is a great sound,
If you can afford to let it play.
6000rpm have I seen,
With cheshire cat grin on face,
40.9p per litre and to boot it's green,
And at such a stonking pace!